Multiplex counting system



Oct. 31, 1950 M, ARDl-'n 2,527,512

MULTIPLEX COUNTING SYSTEM Filed Aug. 14, 1947 MEM/WML PDI/VG' COUNTER f 7'0 TAL SI1/EEP Patented Oct. 31, 17950 UNITED STATE MULTIPLEX COUN TIN G SYSTEM Maurice Arditi,v New York, N. Y., assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application August 14, 1947, Serial No. 768,574

Claims.

more particularly to coincidence counting-'of nuclear particles as registered by Geiger-Muller counters. Y

Y The frequency to which a mechanical counter can respond is limited by the inertia of its mov- Iing parts. For high speed counting it is necessary 'to design circuits in which the relay operates once -for aY relatively largevnumber of impulses. Thus, lif --the mechanical counter, capable of operating at a maximum frequency of 20 per second, is called upon to count'only each tenth pulse, for instance. the device will be capable of counting ra maximum of 200 impulses per second. In order -to be'able to vcount at high speed in applica- Vtions where the phenomena to be registered are of a random nature such as radio-active disintegratiomthat is thelcounting of nuclear par` ticles, which constitute a phenomenon with random fluctuations. a tube has been proposed 4'which is similar to a cathode ray tube and which includes. an apertured plate Vand a dynode.y VA Geiger-Muller counter (hereinafter referred to as a' G-M counter) is placed in the grid circuit ofthe cathode ray tube and a mechanical recording counter in the dynode circuit. Provision is also made for a continuous and cyclical linear sweep of the electron beam across the aperture plate. When a nuclear particle or any other ionizing agent strikes the G-M counter and effects its discharge, the grid of the cathode ray tube, normally biased negatively for non-opera- "tion, receives a' positive pulsewith a resultant "current flow through the tube. -If this occurs at Van instant when the beam passes through vthe slot in the aperture plate and strikes the'dynode. the mechanical counter inthe circuit will register the pulse. Ifthe ionization of the G-M counter occurs at a time when the beam does not intercept the slot, the particle will not be registered. 'Over a period of time suilicientlyA large so that the 'calculus of probability could'be applied, the percentage of misses will be substantially in the ratio of the width of the'linear sweep to the width of the slotf- By'a'proper choice of the ratio of the width ofthe sweep to the width of the slot, a large number of particles vper second can be counted,

f'even if the'response of the mechanical counter is of the order of 20 to 60 per second. The accuracy of measurement is known according to the "assumption of a random distribution. One of the problems in nuclear physics which arises at times and which has presented` certain difficulties is that of coincidence counting. n It an object ofthe present invention to provide a method and apparatus for .counting coincidences and particularly those of. nuclear particles. I It is another object to provide apparatusfor counting the coincidences of nuclearparticles at physically different locations. f f A further object is to provide an apparatus-of the type referred to which utilizes several G-M counters placed at suitableV dilerentr locations making use of a single cathode ray deflection tube. f A still further object is to providea counting circuit which employs a factor of probability in counting the number of coincidences normally beyond the capability ofmechanicalcounter's. f-

A still further object is to provide a counting system which is capable of registering extremely high counts. In accordance with certain features of the in*- vention I provide a number of G-M counters which are placed in the grid circuit of a cathode ray tube modied to include a suitableraperture plate and dynode. These G-M counters are connected to the grid in seriesV with'suitable delay lines which progressively delay the respective pulses of the various counters with,respect to each other. Mechanical counters are provided f in the circuit of the dynode corresponding vto the slot arrangement used. which ordinarily includes a slot for each of the G-M counters.' If there is a coincidence between nuclear Aparticles 'affecting two or more of the G-M counterswithin Vcertain predetermined time limits the mechan ical counters corresponding to the respective G-M counters will provide a record; the number of co- Vincidences are recorded on the mechanical counters following the'first one which registers the total number of particles. The systemA lends itself to the utilization of more than two counters lby the inclusion of suitable delay lines to the grid tion will become apparent and theinvention will be best understood from the following description of embodiments thereof, reference being had to the drawings, in which:

Fig. 1 is a schematic representation of va system for counting the frequency of occurrence vof nu,-

clear particles; I

2 is a schematic representation of a counting system for recording the number of coincidences of nuclear particles at Various locations;

Fig. 3 is a schematic showing of various types of aperture plates for the systems of Figs. 1 and 2; and

Fig. 4 is a representation of the relation of the apertured'plate and the sweepfof the cathode ray tube. I i

Referring to the drawings, the representation in Fig. 1 for counting nuclear particles, comprises a tube I similar to a cathode ray `tube which includes a cathode 2, a control grid 3, anv

' -relation of the width of the sweep to the width electron gun 4, deflection plates 5, an aperture Y.:

plate E, and a dynode The GeM'counter indicated at 8 is placed in the grid circuit of the cathode ray tube. counter, as at 9, is provided in the dynode circuit. A suitable saw-tooth generator I providing va sweep of the type shown at II, is tied to the deectionplates y'togive a continuous linear sweep across fthe aperture platez which is provided with a longitudinal'rectangular slot I2. Normally the grid 3 ofthe cathode ray tube isbiased negatively by Ameans of a suitable potential'supply indicated at I3, whereby current -is prevented from flowing through the tube. p Y

In case of.ionization of the space betweenfelectro'des I4 and I5 of theG-M counter 3 due to the presence of an ionizing agent such as a nuclear particle, a discharge is obtained between the two electrodes I4 .and I5 due to their being biased for a difference of potential by means of a source at I6 and a suitable dropping resistance II connected to -thesourc'e Ii-3. grid to receive a positive pulse therebypermittingvcurrent to flow through the tube. Such an impulse will be registered in the mechanical counter 9 if at that time the beam passes through thefslot I2 thereby striking the dynode. No count isregistered if the beam during the occurrence of the impulses on thegrid 3 is outside of the confines of the slot I2.

A simple coincidence counting system is illus.-

trated-in Fig. 2. Here, a cathode ray 4deflection .Such a discharge causes the r The recording mechanical v providea variable rate of sweep as indicated 4by the .arrow thereon. The G-M counters I24: and 25 are joined to the vsecond* grid A22throughisuitable delay lines 21. The delay lines have the purl. pose of delaying the pulses originating at the respective -G-M counters by a time interval'which equals the Ltime for travel of the cathode ray beam spot from the aperture corresponding .sto the first counter to the vaperture corresponding tothe `second counter, and so forth.V A

In-order t0 provide a betterfappreciationrof the working of the counting system of Fig.. 1,fthe-re'- lation `ofthe sweep of the beam to the slotorslots of the -aperture Vplate is illustrated in Fig- 4. AIn Fig. 4a is indicated schematically the front or viewing end 0f the cathode ray tube indicating'fat 28 va vtypical slot in the aperture plate, and-at `.'29 the extent and location of travel of the beam as it impinges on the aperture plate of the tube.

"Practical :dimensions Kare shown for theslot to comprise a width of 3 mm. and 25 mm. 4for the Yof the slot is indicated in Fig. 4b. The sweep Voltage characteristic is indicated at 30 and the relative position of the slot at 3l. The ratio of multiplication in this case would be 104/50=200. If less accuracy is permissible a smaller ratio of -multiplication lcan be obtained by changing the sweep frequency for instance.

'Greater accuracy may also be obtained -by the use of several slots and several dynodes, each dynode being connected to a separate mechanicalzcounter. Y Variations of such an aperture plate are shown `in Fig. 3.

Diierent multiplication factors could ybe -ob tained in the 'same tube by using anaperture plate ywith several slots of a different aperture widthfas in Fig. 3b, or one slot of variableaperture width with only one dynodev and one mechanical counter at as Fig. 3c, which-may also be coupled to several dynodes and .several mechanical counters. By using one pair of deection plates to put the spot at diiferent levels in the aperture plate, different degrees oi sensitivity may thus beobtained. l

A circular sweep could be used `withseveral slots in the `aperture plate and corresponding dynode's reach with its separate mechanical coun.- ter in vaccordance with Fig. 3d. ,.-Differentsensitivities could also be-obtained with an aperture plate having slots of `different aperture fwidth alongv theradius as in Fig. 3e. `By increasing or decreasing the radius vof the circular sweep, sensitivity vmay be changed easily.

Withreference tothe coincidence counter 4sys,- tem shown in Fig. 2, the delay'line of the .second counter delays the pulses -coming therefrom -and` whichv are -coincidental with those at the first counter by a time which is equal .to that of the travel of the spot from the aperture vassociated with the Yfirst counter-to the aperture associated with the second lcounter. .As thegr-id receives the positive `impulse from the `rst counter, the count `will be recorded by the rstofethe mechanical counters. At the Sametime this positive-,pulse will start the operation of the linear sweep generator'to 'sweepg the beam lacross the aperture plate. The speed of the sweep should :be made such that the vspot will make a completevsweep of the whole aperture plate in less thanZlO-v-4 seconds, vto avoid .fmisses If =the number-nf counts is,.to0-high, high speed circuitcounting of the :type shown in Fig. l -mayy be -11sed.- vSubsequently the grid again becomesanegative.andthe current -is cut off, but Vafter a time-corresponding .to the travel between -tworslotshas elapsedl-the pulsesvfrom the G-.Mcounter-Zfi, delayed Vbyrdelay lines, Vwill make the grid `22 positiveagainandlthe .mechanical-.counter .associated with the- Second slot will record.' the count. VVIt is yto be understood that a positive pulse applied to either grid 3 or 22 will initiate the electron beam but only a posi'- tive pulse from the rst counter v23 can Startoperation of the switch generator. This secondngri'd `22 has vbeen provided so as "to avodfthareac'tlvation of the sweep generator by impulsesofthe 'G-M coun'ters'otherV than the flrst'one." The nmber of coincidences will be recorded on the mechanical counter associated with the second slot, the first mechanical counter recording the total number of particles. Coincidence counting with more than two G-M counters may be accomplished easily by providing delay lines with increasing delays from one to the other corresponding to the time of travel of the spot from one aperture to the others. Circular sweep and several slot arrangements similar to those shown in Fig. 3 can be used. In considering a simple coincidence counting system consisting of two G-M counters, the fact should be kept in mind that a swift ionizing particle which might produce discharges in two counters would have a velocity of at least about 109 cm./sec. If the counters are less than a meter apart the ionization will be produced in bothwithin 10*7 sec of each other. Such a small interval may generally be neglected. It so happens, however, that the initiation of the discharge in a G-M counter, or the separation of the ions in an ionization chamber, occupies a finite time and it is found that impulses must be regarded as coincident if they are timed within an interval which, according to circumstances, amounts usually to one or a few microseconds.

Accordingly, while I have described above the principles of my invention in connection with specific apparatus, such as Geiger-Muller cletectors and particular modifications thereof, it is to be clearly understood that other sources of impulses may be used and that this description is made only by way of example and not as a limitation on the scope of my invention.

What is claimed is:

1. A system for counting the coincidental occurrence of given phenomena. on at least two spaced apart locations, comprising separate counting means corresponding to each of said locations, source of energy conversion comprising means for activating said counting means, means for controlling the successive application of energy to said counting means, means providing energy impulses for controlling the application of energy from said source to each of said counting means in response to the occurrence of a given one of said phenomena at each of said locations, and means for separating said impulses due to coincidentally occurring phenomena in respect to said separate counting means.

2. A system according to claim 1, wherein said counting means corresponding to each location comprises a mechanical recording counter having electrically energizable means for operation thereof.

3. A system according to claim l, wherein said activating means comprises a cathode ray tube including dynode means and a corresponding aperture plate and separate output circuits therefore connected to said counting means respectively.

4. A system according to claim 1, wherein said impulse providing means includes a Geiger-Muller nuclear energy 'detector for each of said locations and connections therefrom to said source.

5. A system according to claim 1, wherein said separating means includes electrical delay lines means for the energy impulses of all but one of said locations and connections including said delay lines to said activating means.

M'AURICE ARDITI.

REFERENCES CITED UNITED STATES PATENTS Name Date Pontecorvo May 23, 1944 Number 

